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Although courts generally want to keep children together after a divorce, different types of custody arrangements work for different families. Split custody -- when siblings live with different parents -- is not a common arrangement, and it can make child support calculations especially complicated. The particular rules and regulations for both support and custody are highly dependent on the facts of your case and the laws of your state.

Custody Overview

Although the terminology and regulations differ by state law, courts generally differentiate between legal and physical custody. Legal custody refers to which parent makes important decisions for the child, such as where the child will go to school or if he should undergo a particular medical procedure. By contrast, physical custody refers to where the child primarily lives. With a split custody arrangement, the divorced parents have more than one child together and each child lives with a different parent. For example, in a split custody arrangement, a father may have sole physical custody of the daughter and the mother has sole physical custody of the son. The parents may have shared legal custody, or legal custody may be similarly split.

Child Support Overview

To calculate the support owed by each parent, states typically follow one of several models for support. The most popular method of support is the income shares model, which considers the income of both parents to ensure that children receive the same amount of support they normally would if their parents were still together. Other states use the percentage of income model, which looks only at the income of the noncustodial parent. A small number of states use the Melson formula, which is similar to the income shares model, but also considers the financial needs of the parents.

Individual Calculation Method

When it comes to child support and split custody, courts may first calculate each parent's obligation individually. In other words, if the mother has custody of the son, the court could first calculate the support the father owes based only on that custody arrangement. If the father has custody of the daughter, the court could then calculate the amount of support the mother owes to the father based only on that relationship. The court will then look at both amounts and subtract the lower payment from the higher payment, and the parent who owes the larger payment will pay the difference to the other parent.

Prorated Calculation

Instead of considering each family unit separately, another method of calculating support in split custody cases is to prorate the support owed to each child based on the total number of children. This typically occurs in states that set the percentage of child support owed based on the number of children. For example, if the guidelines provide that parents must pay 30 percent of their income if they have three children, and the father has custody of only one of the children, the father will pay 20 percent of his income towards child support, while the mother will pay 10 percent. Again, the parent with the larger support obligation will pay the difference between the two amounts.

About the Author

Elizabeth Rayne earned her J.D. from Penn State University and has been practicing law since 2009, advising clients on issues ranging from employment law to nonprofit management. For two years, she served as a contributing editor for the "Vermont Environmental Monitor."